how to login as root

On most linux distributions you can't, just use type su root in a terminal, to gain a root terminal session then run any programs you need from there. (Such as nautilus, gedit excetra), the other way is to put sudo in front of each command you want to run. Although if you are running a graphical application, (instead of one that just prints text in the terminal), you should use gksudo in front of the command. The simple answer is that it is impossible to properly login as root, however you can temporally gain root privalages.

Please read this:

https://help.ubuntu.com/community/RootSudo

hi,
just try
sudo su - root
it will aske to set the root password, set the password and then you will be able to login as root user :)

Or use;

sudo -i

You will then be root with your user configs and environment. You don't need to log in as root, nor is it advised. The sooner you forget about root, the better